Tuberculosis afflicts millions of people, in the United States and other countries. It is a common latent condition, primarily threatening for those with weak immune systems. It is therefore important for doctors to be able to accurately and quickly diagnose tuberculosis in patients.
Many methods are available to screen for the bacterium that causes tuberculosis, but almost all of them are slow and/or prone to error. Many false negatives (more than 40% in one study) and false positives (leading to unnecessary treatment) occur with the methods typically used in the clinic.
There is clearly a need for a fast and reliable tuberculosis test. Addressing this need, Mathias Frank and coworkers at Lawrence Livermore National Laboratory and Michigan State University have used SPAMS (single-particle aerosol mass spectrometry) to detect tuberculosis bacteria.
Detecting tuberculin bacteria with SPAMS.
Mycobacterium tuberculosis cells were grown in the laboratory, aerosolized, and directly analyzed by mass spectrometry. No additional chemicals were required. Particles between approximately 1 and 10 micrometer diameter were detected, based on particle mass, charge, and fluorescence.
Herein, only particle mass was considered, but the other two detection factors are useful if there is much background interference. One source of background interference was from common ion molecules, such as potassium, but such known and common molecules were excluded from analysis.
In order to determine average instrument response, 50 spectra for each sample (tuberculosis bacteria, another bacterial strain, laboratory growth medium, and combinations of each) were obtained. The instrument was able to clearly distinguish between tuberculosis bacteria, related but non-tuberculin bacteria, and background particles.
Success and limitations of SPAMS.
Positive identification of known tuberculosis samples was approximately 51% to 69% with SPAMS, depending on the background content. False identifications are more common when tuberculin bacteria are mixed in with similar but non-tuberculin bacteria. However, since multiple false identifications with one sample are rare (just as flipping a coin five times and getting tails five times is rare), the method is accurate as long as multiple positive readings are obtained.
This is not yet a clinical test, since bacterial samples were grown in the laboratory rather than obtained from real patients. Bacterial concentrations can vary by a factor of 1000 in the real world, and are typically much less than the sample concentrations used in this study.
SPAMS is not yet ready to replace tuberculosis diagnosis using other methods such as microscopic visualization of the bacteria or bacterial DNA amplification. Additionally, mass spectra instruments (of which SPAMS is one) can be very expensive. However, because SPAMS has the advantages of being rapid and not requiring extra chemicals for detection, with further development it may become a standard diagnostic tool for detecting tuberculosis bacteria and other pathogens.
for more information:
Adams, K. L.; Steele, P. T.; Bogan, M. J.; Sadler, N. M.;
Martin, S. I.; Martin, A. N.; Frank, M. Reagentless detection of
Mycobacteria tuberculosis H37Ra in respiratory effluents in minutes.
Anal. Chem. 2008, 80, 5350-5357.